Nowadays, more and more people read files (e.g., web pages) on a mobile communication device, such as a smart phone, a tablet or a computer. Sometimes, the file may not be optimized for displaying on a screen of the mobile communication device. For example, the file may be wider than the screen, in which case, before starting to read next lines, people usually have to move a display window from a rightmost side of the file long-distance back to a leftmost side of the file, by pressing a left/right key on a keyboard or a sliding bar on a touch screen of the mobile communication device.